The world's boldest effort yet to hold North Korea and leader Kim Jong Un accountable for alleged crimes against humanity moved forward Tuesday at the United Nations, where a Pyongyang envoy threatened further nuclear tests.

South Korea on Wednesday formally launched a new safety agency in the wake of April's ferry sinking that killed more than 300 people, mostly teenage students, and exposed shortcomings in disaster response.

The bridge was supposed to be a key link for trade and travel between China's underdeveloped northeast provinces and a much-touted special economic zone in North Korea — so key that Beijing sank more than US$350 million into it.

An anxious North Korea will see Tuesday how the boldest effort yet to bring its leaders to account for alleged crimes against humanity will move forward, as the U.N. General Assembly's human rights committee votes on a resolution that demands the country's referral to the International Criminal Court (ICC).

South Korea's President Park Geun-hye on Tuesday nominated a retired navy general as head of a new broader safety agency to be created in the aftermath of April's ferry sinking that killed more than 300 people.

The U.S. intelligence chief who flew to North Korea on a secret mission to free two Americans said there is “the potential for change” in the secretive state, in a rare window into the murky world of Pyongyang diplomacy.

A U.N. investigator Friday ruled out any compromise on efforts to have North Korea answer formal charges of crimes against humanity, saying holding the regime to account, including supreme leader Kim Jong Un, was “paramount.”

A South Korean court on Tuesday handed a 36-year prison sentence to the captain of a sunken ferry, saying he was professionally negligent and abandoned his passengers during the disaster in April that killed more than 300 people.

US. President Barack Obama is squelching speculation that the release of two Americans held in North Korea might pave the way for a new round of nuclear talks, saying the U.S. needs more than “small gestures” before reopening a high level of dialogue with Pyongyang.

Two Americans released from captivity in North Korea returned to the United States late Saturday after their departure was secured through a secret mission by the top U.S. intelligence official to the reclusive nation.

Nuclear-armed North Korea has started operating a new plant inside its uranium enrichment complex, boosting its capacity to generate fuel that could be used to make atomic weapons, a report said Wednesday.